1. Field of the Invention
The present invention relates generally to implantable cardioverter defibrillators (ICDs) and, more particularly, to preserving ICD functionality in the event of lead failure.
2. Background Art
An implantable cardiac device is a medical device that is implanted in a patient to monitor electrical activity of a heart and to deliver appropriate electrical and/or drug therapy, as required. Implantable cardiac devices include, for example, pacemakers, cardioverters, defibrillators, and the like. The term “implantable cardioverter defibrillator” or simply “ICD” is used hereinafter to refer to any implantable cardiac device.
The ICD includes one or more electrodes that interact with the heart. Before delivering a signal to the heart from the ICD via the electrodes, it is desirable to first check the state of a signal path to determine, for example, if a low impedance or short-circuit like condition exists. A short-circuit like condition can be caused by an electrode touching a housing of the ICD, possibly due to rubbing between the electrode and the housing that has damaged the electrode insulation; two electrodes touching because insulating material between them has worn through; subclavicular crushing of electrodes against each other; displacement or dislodgement of an electrode; and from other situations. Typically, if a short-circuit like condition exists in the signal path, conventional devices either switch to a different electrode configuration (in an effort to find a non short-circuit signal path) or simply stop delivery of the therapy signal to the heart (to prevent damage to the ICD output circuitry). There are times, however, when an effective, alternate lead configuration is not available. Furthermore, failing to deliver therapy can be problematic if the therapy signal was required to sustain a patient's life.
What is needed is a system and method that overcomes deficiencies of known systems.